#include<iostream>
#include<vector>
#include<algorithm>

using namespace std;

int firstMissingPositive(vector<int>& nums) {
    int n = nums.size();
    for (int i = 0;i < n;i++)
    {
        while (nums[i] > 0 && nums[i] <= n && nums[nums[i] - 1] != nums[i])
        {
            swap(nums[nums[i] - 1], nums[i]);
        }
    }
    for (int i = 0;i < n;i++)
    {
        if (nums[i] != i + 1)
        {
            return i + 1;
        }
    }
    return n + 1;
}

int main()
{
    vector<int> nums{ 3,4,-1,1 };
    cout << firstMissingPositive(nums) << endl;
    return 0;
}